Imaging lens system and imaging device comprising seven lenses of −−++−+− refractive powers

ABSTRACT

A vehicle-mounted wide-angle lens that simultaneously achieves a high resolution necessary for sensing, a size small enough to be mounted on a vehicle, and a low price. An imaging lens includes, sequentially from the object side, a first lens having a negative power and being concave on the image side, a second lens having a negative power and being concave on the image side, a third lens having a positive power and being convex on the object side, an aperture stop, a fourth lens having a positive power and being convex on the image side, a fifth lens, a sixth lens whose object side is bonded to the image side of the fifth lens and a seventh lens having a negative power and being convex on the image side, and the fourth lens is an aspheric glass lens.

TECHNICAL FIELD

The present invention relates to an imaging lens system and an imagingdevice.

BACKGROUND ART

The use of a vehicle-mounted wide-angle lens is changing from viewing tosensing today. Sensing requires the resolution necessary for imageanalysis, and therefore high-resolution images in megapixels are needed.Further, performance variation with temperature is seen as important fora vehicle-mounted wide-angle lens. For example, Patent Literature 1discloses a wide-angle lens for vehicle use.

On the other hand, there is a need for a small and inexpensivevehicle-mounted wide-angle lens. Thus, the market demands ahigh-performance, small-size and low-price vehicle-mounted wide-anglelens.

CITATION LIST Patent Literature

PTL1: Japanese Unexamined Patent Application Publication No. 2014-102291

SUMMARY OF INVENTION Technical Problem

However, to achieve a vehicle-mounted wide-angle lens with highresolution and enhanced performance based on temperature, glass lensesare heavily used, which results in a large-size, expensive camera.Therefore, it has not been able to produce a vehicle-mounted wide-anglelens that simultaneously achieves a high resolution necessary forsensing, a size small enough to be mounted on a vehicle, and a lowprice.

Solution to Problem

An imaging lens system according to one embodiment includes,sequentially from an object side, a first lens having a negative powerand being concave on an image side, a second lens having a negativepower and being concave on the image side, a third lens having apositive power and being convex on an object side, an aperture stop, afourth lens having a positive power and being convex on the image side,a fifth lens, a sixth lens whose object side is bonded to the image sideof the fifth lens, and a seventh lens having a negative power and beingconvex on the image side, wherein the fourth lens is an aspheric glasslens.

Preferably, in the imaging lens system according to one embodiment, thefourth lens may have the highest power out of lenses having a positivepower among the first lens to the seventh lens.

Preferably, in the imaging lens system according to one embodiment, afollowing expression (2) may be satisfied, where a focal length of thefourth lens is f4 and a focal length of an entire lens optical system isf,2.8<f4/f<3.5  (2).

Preferably, in the imaging lens system according to one embodiment, afollowing expression (1) may be satisfied, where a focal length of thefifth lens is f5 and a focal length of an entire lens optical system isf,−3.0<f5/f←2.2  (1).

Preferably, in the imaging lens system according to one embodiment, theimage side of the fifth lens and the object side of the sixth lens mayhave an aspheric shape.

Preferably, in the imaging lens system according to one embodiment, thesecond lens, the third lens, the fifth lens, the sixth lens and theseventh lens may be plastic lenses.

An imaging device according to one embodiment includes the imaging lenssystem according to any one of the above, a lens barrel that holds theimaging lens system, a flat-plate cover glass placed on an object sideof the imaging lens system, and an image sensor placed at an imagelocation of the imaging lens system.

Advantageous Effects of Invention

A vehicle-mounted wide-angle lens and an imaging device according to thepresent invention simultaneously achieve a high resolution necessary forsensing, a size small enough to be mounted on a vehicle, and a lowprice.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of an imaging lens system according to anexample 1;

FIG. 2A is a longitudinal aberration diagram of the imaging lens systemaccording to the example 1;

FIG. 2B is a field curvature diagram of the imaging lens systemaccording to the example 1;

FIG. 2C is a distortion diagram of the imaging lens system according tothe example 1;

FIG. 3 is a sectional view of an imaging lens system according to anexample 2;

FIG. 4A is a longitudinal aberration diagram of the imaging lens systemaccording to the example 2;

FIG. 4B is a field curvature diagram of the imaging lens systemaccording to the example 2;

FIG. 4C is a distortion diagram of the imaging lens system according tothe example 2;

FIG. 5 is a sectional view of an imaging lens system according to anexample 3;

FIG. 6A is a longitudinal aberration diagram of the imaging lens systemaccording to the example 3;

FIG. 6B is a field curvature diagram of the imaging lens systemaccording to the example 3;

FIG. 6C is a distortion diagram of the imaging lens system according tothe example 3;

FIG. 7 is a sectional view of an imaging lens system according to anexample 4;

FIG. 8A is a longitudinal aberration diagram of the imaging lens systemaccording to the example 4;

FIG. 8B is a field curvature diagram of the imaging lens systemaccording to the example 4;

FIG. 8C is a distortion diagram of the imaging lens system according tothe example 4;

FIG. 9 is a sectional view of an imaging lens system according to anexample 5;

FIG. 10A is a longitudinal aberration diagram of the imaging lens systemaccording to the example 5;

FIG. 10B is a field curvature diagram of the imaging lens systemaccording to the example 5;

FIG. 10C is a distortion diagram of the imaging lens system according tothe example 5; and

FIG. 11 is a sectional view of an imaging device according to an example6.

DESCRIPTION OF EMBODIMENTS

An imaging lens system and an imaging device according to examples aredescribed hereinafter.

Example 1: Imaging Lens System

FIG. 1 is a sectional view of an imaging lens system according to anexample 1. In FIG. 1, an imaging lens system 11 includes, sequentiallyfrom the object side, a first lens L1 having a negative power and beingconcave on the image side, a second lens L2 having a negative power andbeing concave on the image side, a third lens L3 having a positive powerand being convex on the object side, an aperture stop STOP, a fourthlens L4 having a positive power and being convex on the image side, afifth lens L5, a sixth lens L6 whose object side is bonded to the imageside of the fifth lens, and a seventh lens L7 having a negative powerand being convex on the image side. Further, the imaging lens system 11includes an IR cut filter 12. IMG indicates an imaging plane.

The first lens L1 is a lens having a negative power. An object-side lenssurface S1 of the first lens L1 has a curved part that is convex to theobject side. An image-side lens surface S2 of the first lens L1 has acurved part that is concave to the object side. The first lens L1 ispreferably made of ground glass.

The second lens L2 is an aspheric lens having a negative power. Anobject-side lens surface S3 of the second lens L2 has a curved part thatis convex to the object side, and an image-side lens surface S4 of thesecond lens L2 has a curved part that is concave to the object side. Thesecond lens L2 is preferably a plastic lens.

The third lens L3 is an aspheric lens having a positive power. Anobject-side lens surface S5 of the third lens L3 has a curved part thatis convex to the object side, and an image-side lens surface S6 of thethird lens L3 has a curved part that is convex to the image side. Thethird lens L3 is preferably a plastic lens.

The aperture stop STOP adjusts the amount of light to pass through. Forexample, the aperture stop STOP is preferably in the form of a platewith a hole.

The fourth lens L4 is an aspheric lens having a positive power. Anobject-side lens surface S9 of the fourth lens L4 has a curved part thatis concave to the image side, and an image-side lens surface S10 of thefourth lens L4 has a curved part that is convex to the image side. Thefourth lens L4 is preferably an aspheric glass lens.

The fifth lens L5 is an aspheric lens having a negative power. Anobject-side lens surface S11 of the fifth lens L5 has a curved part thatis convex to the object side, and an image-side lens surface S12 of thefifth lens L5 has a curved part that is concave to the object side. Thefifth lens L5 is preferably a plastic lens.

The sixth lens L6 is an aspheric lens having a positive power. Anobject-side lens surface S13 of the sixth lens L6 has a curved part thatis convex to the object side, and an image-side lens surface S14 of thesixth lens L6 has a curved part that is convex to the image side. Thesixth lens L6 is preferably a plastic lens.

The image-side lens surface of the fifth lens L5 and the object-sidelens surface of the sixth lens L6 are bonded by an ultraviolet curingadhesive, and the fifth lens L5 and the sixth lens L6 form a compoundlens. The spacing between the image-side lens surface of the fifth lensL5 and the object-side lens surface of the sixth lens L6 graduallybecomes wider as it goes from the optical axis to the outer periphery soas to release air bubbles in the adhesive to the outside. The combinedpower of the fifth lens L5 and the sixth lens L6 is a positive power.

The seventh lens L7 is an aspheric lens having a negative power. Anobject-side lens surface S15 of the seventh lens L7 has a curved partthat is concave to the image side, and an image-side lens surface S16 ofthe seventh lens L7 has a curved part that is convex to the image side.The seventh lens L7 is preferably a plastic lens.

The IR cut filter 12 is a filter that cuts out infrared light.

The property data of the imaging lens system 11 is describedhereinafter.

First, Table 1 shows lens data of each lens surface in the imaging lenssystem 11. In Table 1, the curvature radius, the surface-to-surfacedistance, the refractive index, and the Abbe number are shown as lensdata. The surface denoted by the symbol “*” indicates an asphericsurface.

TABLE 1 Lens Parameter Surface-to- nd Curvature surface (Refractive vd(Abbe radius distance index) number) 1st surface 15.991 1.000 1.804 46.52nd surface 4.378 2.564 3rd surface 15.662 1.281 1.545 56.2 * 4thsurface 1.861 1.717 * 5th surface 42.187 2.565 1.661 20.4 * 6th surface−5.885 0.545 * (STOP) 7th INFINITY 0.030 surface 8th surface INFINITY0.497 9th surface −23.411 1.919 1.553 71.7 * 10th surface −2.531 0.17211th surface 26.652 1.594 1.661 20.4 * 12th surface 2.440 0.020 1.50251.0 * 13th surface 2.440 2.977 1.545 56.2 * 14th surface −3.973 0.100 *15th surface −11.079 0.630 1.545 56.2 * 16th surface −81.773 0.100 *17th surface INFINITY 0.700 1.517 64.2 18th surface INFINITY 1.588

The aspheric shape used for a lens surface is represented by thefollowing expression when z is a sag, c is the inverse of a curvatureradius, k is a constant of the cone, r is a height from the optical axisZ, and the 4th-order, 6th-order, 8th-order, 10th-order, 12th-order,14th-order and 16th-order aspheric coefficients are α4, α6, α8, α10,α12, α14 and α16, respectively.

$z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {\alpha_{1}r^{2}} + {\alpha_{2}r^{4}} + {\alpha_{3}r^{6}} + {\alpha_{4}r^{8}} + {\alpha_{5}r^{10}} + {\alpha_{6}r^{12}} + {\alpha_{7}r^{14}} + {\alpha_{8}r^{16}}}$

Table 2 shows aspheric coefficients for defining the aspheric shape ofan aspheric lens surface in the imaging lens system 11 of the example 1.In Table 2, “−6.522528E-03” means “−6.522528×10⁻³”, for example.

TABLE 2 Aspheric coefficients 3rd surface 4th surface 5th surface 6thsurface 9th surface 10th surface k   0.000000E+00 −0.584698029 0  0.000000E+00   0.000000E+00 −0.014941829 α4 −3.212063E−03  1.537786E−03   5.007120E−03   8.551587E−03 −8.173230E−03  5.043637E−03 α6   9.514080E−05 −1.067514E−03 −2.332544E−04−2.371804E−03 −1.237787E−03 −3.462408E−04 α8 −1.138907E−06  3.593001E−06   1.323046E−04   1.184827E−03 −1.891273E−04  5.526840E−05 α10 −1.865120E−08   0.000000E+00   0.000000E+00−1.454256E−04   0.000000E+00   0.000000E+00 α12   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00 α12   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00 α16   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00 11th surface 12th surface 13th surface 14th surface 15thsurface 16th surface k 0 −2.095437E−01 −2.095437E−01 0   0.000000E+00 0α4   2.779169E−03   6.975202E−03   9.975202E−03   2.363654E−02  1.150292E−02 −1.331737E−02 α6   1.548943E−04   1.125342E−04  1.125342E−04 −4.434208E−03 −2.329412E−03   3.993663E−03 α8  0.000000E+00 −1.626998E−04 −1.626998E−04   6.404750E−04   5.690953E−05−9.674284E−04 α10   0.000000E+00   0.000000E+00   0.000000E+00−2.956144E−05   0.000000E+00   9.632779E−05 α12   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00−3.320306E−06 α12   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   6.930747E−09 α16   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00

FIG. 2A is a longitudinal aberration diagram of the imaging lens systemin the example 1. FIG. 2B is a field curvature diagram of the imaginglens system in the example 1. FIG. 2C is a distortion diagram of theimaging lens system in the example 1. As shown in FIGS. 2A to 2C, thehalf angle of view is 99°, and the F-number is 2.0 in the imaging lenssystem 11 of the example 1. In the longitudinal aberration diagram ofFIG. 2A, the horizontal axis indicates a position where a light rayintersects the optical axis Z, and the vertical axis indicates a heightof pupil diameter.

In the field curvature diagram of FIG. 2B, the horizontal axis indicatesa distance along the optical axis Z, and the vertical axis indicates theimage height (angle of view). Further, in the field curvature diagram ofFIG. 2B, Sag indicates the curvature of field on a sagittal plane, andTan indicates the curvature of field on a tangential plane. As shown inthe field curvature diagram of FIG. 2B, the curvature of field iscorrected appropriately in the imaging lens system 11 of this example.The imaging lens system 1 thereby achieves a high resolution.

In the distortion diagram of FIG. 2C, the horizontal axis indicates theamount of distortion (%) of an image, and the vertical axis indicatesthe image height (angle of view). The field curvature diagram of FIG. 2Band the distortion diagram of FIG. 2C show results of simulation using alight ray with a wavelength of 588 nm.

Table 3 shows results of calculating property values of the imaging lenssystem 11 of the example 1. Table 3 shows the property values (acombined focal length f₁₂ of the first lens L1 and the second lens L2, acombined focal length f₂₃ of the second lens L2 and the third lens L3, acombined focal length f₃₄ of the third lens L3 and the fourth lens L4, acombined focal length f₄ of the fourth lens L4 and the fifth lens L5, acombined focal length f₅₆ of the fifth lens L5 and the sixth lens L6,and a combined focal length f₆₇ of the sixth lens L6 and the seventhlens L7), f₄/f, and f₅/f when the focal length of the whole lens systemis f, the focal length of the first lens L1 is f₁, the focal length ofthe second lens L2 is f₂, the focal length of the third lens L3 is f₃,the focal length of the fourth lens L4 is f₄, the focal length of thefifth lens L5 is f₅, the focal length of the sixth lens L6 is f₆, andthe focal length of the seventh lens L7 is f₇ in the imaging lens system11. Each focal length is calculated using a light ray with a wavelengthof 588 nm.

TABLE 3 Example 1 Property Item Value Unit F No 2.0 — Optical length20.000 mm Whole system f 1.574 mm f₁ −7.796 mm f₂ −4.005 mm f₃ 7.986 mmf₄ 4.966 mm f₅ −4.173 mm f₆ 6.657 mm f₇ −23.583 mm f₁₂ −2.065 mm f₂₃−32.150 mm f₃₄ 3.834 mm f₄₅ 5.702 mm f₅₆ 8.460 mm f₆₇ 9.133 mm f₄/f3.156 f₅/f −2.65

As described above, in the imaging lens system of the example 1, becausethe fourth lens that is immediately next to the aperture stop is a glasslens, it is possible to widely set the refractive index and the Abbenumber and thereby facilitate the correction of aberrations, andtherefore the lenses other than this lens can be plastic lenses, whichmakes it possible to simultaneously achieve a high resolution necessaryfor sensing, a size small enough to be mounted on a vehicle, and a lowprice. Particularly, in the case of producing a high-resolution andsmall-size wide-angle imaging lens system with a lens structure having 7or more lenses, the price of the imaging lens system increases due to anincreased number of aspheric glass lenses. The imaging lens system ofthe example 1 can use inexpensive plastic lenses except for the fourthlens that is immediately next to the aperture stop, thereby achievingprice reduction.

Further, in the imaging lens system of the example 1, because the fourthlens that is immediately next to the aperture stop is a glass lens,variation in resolution due to out-of-focus caused by temperature changeis reduced.

Lenses that constitute an optical system are classified into positivelenses that constitute an image-forming system and negative lenses thatconstitute a correction system. As is obvious from Table 3, the fourthlens has the shortest focal length and has the highest positive poweramong the positive lenses. By using glass, rather than plastic, for thishighest-power lens, it is possible to appropriately avoid out-of-focuscaused by temperature change in the entire optical system.

Further, the range of the Abbe number of an aspheric glass lens of thefourth lens preferably satisfies the following expression (4). Byreducing chromatic dispersion in the fourth lens with the highest power,it is possible to improve the properties of the entire optical system.ν4≥53  (4)

When the focal length of the fourth lens is f4 and the focal length ofthe entire lens optical system is f, it is preferred to satisfy thefollowing expression (2).2.8<f4/f<3.5  (2)

When the upper limit of the expression (2) is exceeded, the correctionof out-of-focus by the fourth lens is insufficient, and the MTF isdegraded. On the other hand, when the lower limit of the expression (2)is exceeded, the correction of out-of-focus by the fourth lens isexcessive, and the MTF is degraded. To make a more effective correction,it is preferred to satisfy the following expression (3).2.9<f4/f<3.3  (3)

Further, in the imaging lens system of the example 1, the fifth lenssatisfies the following conditional expression (1), which preventsexcessive chromatic aberration correction and thereby avoids the wholeimage degradation, and also prevents insufficient chromatic aberrationcorrection and thereby avoids the whole image degradation as well.−3.0<f5/f←2.2  (1)

(f5 is the focal length of the fifth lens, and f is the focal length ofthe entire system)

Note that, when the lower limit of the above expression (1) is exceeded,the power of f5 increases and the chromatic aberration correction isexcessive, which causes the whole image degradation. On the other hand,when the upper limit of the above expression (1) is exceeded, the powerof f5 decreases and the chromatic aberration correction is insufficient,which also causes the whole image degradation.

Further, the F-number is small, which produces a bright lens.Furthermore, the lenses closer to the image than the fourth lens areless affected by spherical aberration and coma aberration.

Example 2: Imaging Lens System

FIG. 3 is a sectional view of an imaging lens system according to anexample 2. In FIG. 3, the same elements as those in FIG. 1 are denotedby the same reference numerals, and the description thereof is omitted.In FIG. 3, an imaging lens system 11 includes, sequentially from theobject side, a first lens L1 having a negative power and being concaveon the image side, a second lens L2 having a negative power and beingconcave on the image side, a third lens L3 having a positive power andbeing convex on the object side, an aperture stop STOP, a fourth lens L4having a positive power and being convex on the image side, a fifth lensL5, a sixth lens L6 whose object side is bonded to the image side of thefifth lens, and a seventh lens L7 having a negative power and beingconvex on the image side. Further, the imaging lens system 11 includesan IR cut filter 12. IMG indicates an imaging plane.

The property data of the imaging lens system 11 is describedhereinafter.

First, Table 4 shows lens data of each lens surface in the imaging lenssystem 11. In Table 4, the curvature radius, the surface-to-surfacedistance, the refractive index, and the Abbe number are shown as lensdata. The surface denoted by the symbol “*” indicates an asphericsurface.

TABLE 4 Lens Parameter Surface-to- nd Curvature surface (Refractive vd(Abbe radius distance index) number) 1st surface 16.046 1.000 1.804 46.52nd surface 4.361 2.631 3rd surface 15.759 1.300 1.545 56.2 * 4thsurface 1.854 1.727 * 5th surface 43.262 2.586 1.661 20.4 * 6th surface−5.470 0.480 * (STOP) 7th INFINITY 0.030 surface 8th surface INFINITY0.501 9th surface −24.265 1.819 1.553 71.7 * 10th surface −2.522 0.155 *11th surface 40.846 1.539 1.661 20.4 * 12th surface 2.178 0.020 1.50251.0 * 13th surface 2.178 2.951 1.545 56.2 * 14th surface −3.950 0.100 *15th surface −11.430 0.705 1.545 56.2 * 16th surface −67.293 0.100 *17th surface INFINITY 0.700 1.517 64.2 18th surface INFINITY 1.655

Table 5 shows aspheric coefficients for defining the aspheric shape ofan aspheric lens surface in the imaging lens system 11 of the example 2.In Table 5, “−6.522528E-03” means “−6.522528×10⁻³”, for example.

TABLE 5 Aspheric coefficients 3rd surface 4th surface 5th surface 6thsurface 9th surface 10th surface k   0.000000E+00 −0.576599838 0  0.000000E+00   0.000000E+00 −0.002225356 α4 −3.222183E−03  1.859319E−03   4.747473E−03   8.022545E−03 −8.321899E−03  4.805045E−03 α6   9.485620E−05 −1.000232E−03 −3.395912E−04−2.035585E−03 −1.895069E−03 −2.964869E−04 α8 −1.143585E−06  1.643372E−05   1.442903E−04   9.170244E−04 −2.310353E−05  6.256485E−05 α10 −7.335783E−09   0.000000E+00   0.000000E+00−1.001551E−04   0.000000E+00   0.000000E+00 α12   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00 α12   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00 α16   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00 11th surface 12th surface 13th surface 14th surface 15thsurface 16th surface k 0 −2.749379E−01 −2.749379E−01 0   0.000000E+00 0α4   2.984886E−03   5.901228E−03   8.901228E−03   2.351106E−02  1.150292E−02 −1.344924E−02 α6   1.962828E−04 −2.425862E−04−2.425862E−04 −4.446172E−03 −2.314576E−03   3.982074E−03 α8  0.000000E+00 −2.972174E−04 −2.972174E−04   6.401527E−04   5.792500E−05−9.682540E−04 α10   0.000000E+00   0.000000E+00   0.000000E+00−2.920476E−05   0.000000E+00   9.633928E−05 α12   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00−3.294368E−06 α12   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   1.569481E−08 α16   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00

FIG. 4A is a longitudinal aberration diagram of the imaging lens systemin the example 2. FIG. 4B is a field curvature diagram of the imaginglens system in the example 2. FIG. 4C is a distortion diagram of theimaging lens system in the example 2. As shown in FIGS. 4A to 4C, thehalf angle of view is 99°, and the F-number is 2.0 in the imaging lenssystem 11 of the example 2. In the longitudinal aberration diagram ofFIG. 4A, the horizontal axis indicates a position where a light rayintersects the optical axis Z, and the vertical axis indicates a heightof pupil diameter.

In the field curvature diagram of FIG. 4B, the horizontal axis indicatesa distance along the optical axis Z, and the vertical axis indicates theimage height (angle of view). Further, in the field curvature diagram ofFIG. 4B, Sag indicates the curvature of field on a sagittal plane, andTan indicates the curvature of field on a tangential plane. As shown inthe field curvature diagram of FIG. 4B, the curvature of field iscorrected appropriately in the imaging lens system 11 of this example.The imaging lens system 11 thereby achieves a high resolution.

In the distortion diagram of FIG. 4C, the horizontal axis indicates theamount of distortion (%) of an image, and the vertical axis indicatesthe image height (angle of view). The field curvature diagram of FIG. 4Band the distortion diagram of FIG. 4C show results of simulation using alight ray with a wavelength of 588 nm.

Table 6 shows results of calculating property values of the imaging lenssystem 11 of the example 2. Table 6 shows the property values (acombined focal length f₁₂ of the first lens L1 and the second lens L2, acombined focal length f₂₃ of the second lens L2 and the third lens L3, acombined focal length f₃₄ of the third lens L3 and the fourth lens L4, acombined focal length f₄₅ of the fourth lens L4 and the fifth lens L5, acombined focal length f₅₆ of the fifth lens L5 and the sixth lens L6,and a combined focal length f₆₇ of the sixth lens L6 and the seventhlens L7), f₄/f, and f₅/f when the focal length of the whole lens systemis f, the focal length of the first lens L1 is f₁, the focal length ofthe second lens L2 is f₂, the focal length of the third lens L3 is f₃,the focal length of the fourth lens L4 is f₄, the focal length of thefifth lens L5 is f₅, the focal length of the sixth lens L6 is f₆, andthe focal length of the seventh lens L7 is f₇ in the imaging lens system11. Each focal length is calculated using a light ray with a wavelengthof 588 nm.

TABLE 6 Example 2 Property Item Value Unit F No 2.0 — Optical length20.008 mm Whole system f 1.601 mm f₁ −7.742 mm f₂ −3.987 mm f₃ 7.508 mmf₄ 4.940 mm f₅ −3.538 mm f₆ 6.553 mm f₇ −25.372 mm f₁₂ −2.040 mm f₂₃−60.081 mm f₃₄ 3.713 mm f₄₅ 6.223 mm f₅₆ 9.137 mm f₆₇ 8.716 mm f₄/f3.086 f₅/f −2.21

As described above, in the imaging lens system of the example 2, becausethe fourth lens that is immediately next to the aperture stop is a glasslens, it is possible to widely set the refractive index and the Abbenumber and thereby facilitate the correction of aberrations, andtherefore the lenses other than this lens can be plastic lenses, whichmakes it possible to simultaneously achieve a high resolution necessaryfor sensing, a size small enough to be mounted on a vehicle, and a lowprice. Further, in the imaging lens system of the example 2, the rangeof f4/f and the range of the Abbe number ν4 of the fourth lens may bethe same as those in the imaging lens system of the example 1. Further,the imaging lens system of the example 2 also has the same effects asthe imaging lens system of the example 1.

Example 3: Imaging Lens System

FIG. 5 is a sectional view of an imaging lens system according to anexample 3. In FIG. 5, the same elements as those in FIG. 1 are denotedby the same reference numerals, and the description thereof is omitted.In FIG. 5, an imaging lens system 11 includes, sequentially from theobject side, a first lens L1 having a negative power and being concaveon the image side, a second lens L2 having a negative power and beingconcave on the image side, a third lens L3 having a positive power andbeing convex on the object side, an aperture stop STOP, a fourth lens L4having a positive power and being convex on the image side, a fifth lensL5, a sixth lens L6 whose object side is bonded to the image side of thefifth lens, and a seventh lens L7 having a negative power and beingconvex on the image side. Further, the imaging lens system 11 includesan IR cut filter 12. IMG indicates an imaging plane.

The property data of the imaging lens system 11 is describedhereinafter.

First, Table 7 shows lens data of each lens surface in the imaging lenssystem 11. Table 7 shows lens data of each lens surface in the imaginglens system 11. In Table 7, the curvature radius, the surface-to-surfacedistance, the refractive index, and the Abbe number are shown as lensdata. The surface denoted by the symbol “*” indicates an asphericsurface.

TABLE 7 Lens Parameter Surface-to- nd vd Curvature surface (Refractive(Abbe radius distance index) number) 1st surface 16.091 1.000 1.804 46.52nd surface 4.351 2.656 3rd surface 15.834 1.310 1.545 56.2 * 4thsurface 1.852 1.736 * 5th surface 41.890 2.604 1.661 20.4 * 6th surface−5.305 0.463 * (STOP) 7th INFINITY 0.030 surface 8th surface INFINITY0.490 9th surface −24.301 1.754 1.553 71.7 * 10th surface −2.515 0.151 *11th surface 62.000 1.508 1.661 20.4 * 12th surface 2.084 0.020 1.50251.0 * 13th surface 2.084 2.933 1.545 56.2 * 14th surface −3.934 0.100 *15th surface −11.687 0.724 1.545 56.2 * 16th surface −59.118 0.100 *17th surface INFINITY 0.700 1.517 64.2 18th surface INFINITY 1.721

Table 8 shows aspheric coefficients for defining the aspheric shape ofan aspheric lens surface in the imaging lens system 11 of the example 3.In Table 8, “−6.522528E-03” means “−6.522528×10⁻³”, for example.

TABLE 8 Aspheric coefficients 3rd surface 4th surface 5th surface 6thsurface 9th surface 10th surface k   0.000000E+00 0 0   0.000000E+00  0.000000E+00 0 α4 −3.235388E−03 −9.676759E−04   4.717586E−03−1.369659E−03 −6.372799E−03 −2.723250E−04 α6   9.392779E−05  2.181954E−05 −2.669468E−04   8.446096E−04 −3.244233E−03   1.148788E−04α8 −1.242726E−06   0.000000E+00   2.137388E−04 −3.634946E−05  8.160340E−04   0.000000E+00 α10 −2.078379E−08   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00 α12  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00 α12   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00 α16  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00 11th surface 12th surface 13th surface14th surface 15th surface 16th surface k 0   0.000000E+00 −2.640209E−010   0.000000E+00 0 α4   3.038881E−03   0.000000E+00   8.842468E−03−4.452736E−03   1.150292E−02   3.976450E−03 α6   2.117974E−04  0.000000E+00 −2.580951E−04   6.390497E−04 −2.307742E−03 −9.688395E−04α8   0.000000E+00   5.842468E−03 −3.234701E−04 −2.934837E−05  5.902903E−05   9.622089E−05 α10   0.000000E+00 −2.580951E−04  0.000000E+00   0.000000E+00   0.000000E+00 −3.312714E−06 α12  0.000000E+00 −3.234701E−04   0.000000E+00   0.000000E+00  0.000000E+00   1.282349E−08 α12   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00 α16  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00

FIG. 6A is a longitudinal aberration diagram of the imaging lens systemin the example 3. FIG. 6B is a field curvature diagram of the imaginglens system in the example 3. FIG. 6C is a distortion diagram of theimaging lens system in the example 3. As shown in FIGS. 6A to 6C, thehalf angle of view is 99°, and the F-number is 2.0 in the imaging lenssystem 11 of the example 3. In the longitudinal aberration diagram ofFIG. 6A, the horizontal axis indicates a position where a light rayintersects the optical axis Z, and the vertical axis indicates a heightof pupil diameter.

In the field curvature diagram of FIG. 6B, the horizontal axis indicatesa distance along the optical axis Z, and the vertical axis indicates theimage height (angle of view). Further, in the field curvature diagram ofFIG. 6B, Sag indicates the curvature of field on a sagittal plane, andTan indicates the curvature of field on a tangential plane. As shown inthe field curvature diagram of FIG. 6B, the curvature of field iscorrected appropriately in the imaging lens system 11 of this example.The imaging lens system 11 thereby achieves a high resolution.

In the distortion diagram of FIG. 6C, the horizontal axis indicates theamount of distortion (%) of an image, and the vertical axis indicatesthe image height (angle of view). The field curvature diagram of FIG. 6Band the distortion diagram of FIG. 6C show results of simulation using alight ray with a wavelength of 588 nm.

Table 9 shows results of calculating property values of the imaging lenssystem 11 of the example 3. Table 9 shows the property values (acombined focal length f₁₂ of the first lens L1 and the second lens L2, acombined focal length f₂₃ of the second lens L2 and the third lens L3, acombined focal length f₃₄ of the third lens L3 and the fourth lens L4, acombined focal length f₄₅ of the fourth lens L4 and the fifth lens L5, acombined focal length f₅₆ of the fifth lens L5 and the sixth lens L6,and a combined focal length f₆₇ of the sixth lens L6 and the seventhlens L7), f₄/f, and f₅/f when the focal length of the whole lens systemis f, the focal length of the first lens L1 is f₁, the focal length ofthe second lens L2 is f₂, the focal length of the third lens L3 is f₃,the focal length of the fourth lens L4 is f₄, the focal length of thefifth lens L5 is f₅, the focal length of the sixth lens L6 is f₆, andthe focal length of the seventh lens L7 is f₇ in the imaging lens system11. Each focal length is calculated using a light ray with a wavelengthof 588 nm.

TABLE 9 Example 3 Property Item Value Unit F No 2.0 — Optical length21.008 mm Whole system f 1.614 mm f₁ −7.707 mm f₂ −3.978 mm f₃ 7.286 mmf₄ 4.928 mm f₅ −3.296 mm f₆ 6.500 mm f₇ −26.867 mm f₁₂ −2.028 mm f₂₃−109.038 mm f₃₄ 3.654 mm f₄₅ 6.559 mm f₅₆ 9.551 mm f₆₇ 8.475 mm f₄/f3.054 f₅/f −2.04

As described above, in the imaging lens system of the example 3, becausethe fourth lens that is immediately next to the aperture stop is a glasslens, it is possible to widely set the refractive index and the Abbenumber and thereby facilitate the correction of aberrations, andtherefore the lenses other than this lens can be plastic lenses, whichmakes it possible to simultaneously achieve a high resolution necessaryfor sensing, a size small enough to be mounted on a vehicle, and a lowprice. Further, in the imaging lens system of the example 3, the rangeof f4/f and the range of the Abbe number v4 of the fourth lens may bethe same as those in the imaging lens system of the example 1. Further,the imaging lens system of the example 3 also has the same effects asthe imaging lens system of the example 1.

Example 4: Imaging Lens System

FIG. 7 is a sectional view of an imaging lens system according to anexample 4. In FIG. 7, the same elements as those in FIG. 1 are denotedby the same reference numerals, and the description thereof is omitted.In FIG. 7, an imaging lens system 11 includes, sequentially from theobject side, a first lens L1 having a negative power and being concaveon the image side, a second lens L2 having a negative power and beingconcave on the image side, a third lens L3 having a positive power andbeing convex on the object side, an aperture stop STOP, a fourth lens L4having a positive power and being convex on the image side, a fifth lensL5, a sixth lens L6 whose object side is bonded to the image side of thefifth lens, and a seventh lens L7 having a negative power and beingconvex on the image side. Further, the imaging lens system 11 includesan IR cut filter 12. IMG indicates an imaging plane.

The property data of the imaging lens system 11 is describedhereinafter. First, Table 10 shows lens data of each lens surface in theimaging lens system 11. In Table 10, the curvature radius, thesurface-to-surface distance, the refractive index, and the Abbe numberare shown as lens data. The surface denoted by the symbol “*” indicatesan aspheric surface.

TABLE 10 Lens Parameter Surface-to- nd Curature surface (Refractive vd(Abbe radius distance index) number) 1st surface 15.926 1.000 1.804 46.52nd surface 4.392 2.503 3rd surface 15.558 1.258 1.545 56.2 * 4thsurface 1.866 1.706 * 5th surface 41.164 2.546 1.661 20.4 * 6th surface−6.362 0.604 * (STOP) 7th INFINITY 0.030 surface 8th surface INFINITY0.547 9th surface −22.285 1.881 1.553 71.7 * 10th surface −2.538 0.178 *11th surface 21.821 1.623 1.661 20.4 * 12th surface 2.667 0.020 1.50251.0 * 13th surface 2.667 2.987 1.545 56.2 * 14th surface −3.990 0.100 *15th surface −10.782 0.630 1.545 56.2 * 16th surface −81.142 0.100 *17th surface INFINITY 0.700 1.517 64.2 18th surface INFINITY 1.591

Table 11 shows aspheric coefficients for defining the aspheric shape ofan aspheric lens surface in the imaging lens system 11 of the example 4.In Table 11, “−6.522528E-03” means “−6.522528×10⁻³”, for example.

TABLE 11 Aspheric coefficients 3rd surface 4th surface 5th surface 6thsurface 9th surface 10th surface k   0.000000E+00 0 0   0.000000E+00  0.000000E+00 0 α4 −3.197780E−03 −1.120732E−03   5.290403E−03−1.941496E−03 −8.349588E−03 −3.707933E−04 α6   9.538701E−05  6.486319E−07 −2.422918E−04   1.071738E−03 −7.695661E−04   3.980456E−05α8 −1.073952E−06   0.000000E+00   1.065674E−04 −1.406919E−04−3.380581E−04   0.000000E+00 α10 −1.120887E−08   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00 α12  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00 α12   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00 α16  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00 11th surface 12th surface 13th surface14th surface 15th surface 16th surface k 0   0.000000E+00 −1.456028E−010   0.000000E+00 0 α4   2.734196E−03   0.000000E+00   1.059262E−02−4.436244E−03   1.150292E−02   3.996097E−03 α6   1.910585E−04  0.000000E+00   1.660877E−04   6.349932E−04 −2.328558E−03 −9.678182E−04α8   0.000000E+00   7.592624E−03   2.890619E−05 −3.089137E−05  5.967373E−05   9.603144E−05 α10   0.000000E+00   1.660877E−04  0.000000E+00   0.000000E+00   0.000000E+00 −3.347762E−06 α12  0.000000E+00   2.890619E−05   0.000000E+00   0.000000E+00  0.000000E+00   3.844783E−09 α12   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00 α16  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00

FIG. 8A is a longitudinal aberration diagram of the imaging lens systemin the example 4. FIG. 8B is a field curvature diagram of the imaginglens system in the example 4. FIG. 8C is a distortion diagram of theimaging lens system in the example 4. As shown in FIGS. 8A to 8C, thehalf angle of view is 99°, and the F-number is 2.0 in the imaging lenssystem 11 of the example 4. In the longitudinal aberration diagram ofFIG. 8A, the horizontal axis indicates a position where a light rayintersects the optical axis Z, and the vertical axis indicates a heightof pupil diameter.

In the field curvature diagram of FIG. 8B, the horizontal axis indicatesa distance along the optical axis Z, and the vertical axis indicates theimage height (angle of view). Further, in the field curvature diagram ofFIG. 8B, Sag indicates the curvature of field on a sagittal plane, andTan indicates the curvature of field on a tangential plane. As shown inthe field curvature diagram of FIG. 8B, the curvature of field iscorrected appropriately in the imaging lens system 11 of this example.The imaging lens system 11 thereby achieves a high resolution.

In the distortion diagram of FIG. 8C, the horizontal axis indicates theamount of distortion (%) of an image, and the vertical axis indicatesthe image height (angle of view). The field curvature diagram of FIG. 8Band the distortion diagram of FIG. 8C show results of simulation using alight ray with a wavelength of 588 nm.

Table 12 shows results of calculating property values of the imaginglens system 11 of the example 4. Table 12 shows the property values (acombined focal length f₁₂ of the first lens L1 and the second lens L2, acombined focal length f₂₃ of the second lens L2 and the third lens L3, acombined focal length f₃₄ of the third lens L3 and the fourth lens L4, acombined focal length f₄₅ of the fourth lens L4 and the fifth lens L5, acombined focal length f₅₆ of the fifth lens L5 and the sixth lens L6,and a combined focal length f₆₇ of the sixth lens L6 and the seventhlens L7), f₄/f, and f₅/f when the focal length of the whole lens systemis f, the focal length of the first lens L1 is f₁, the focal length ofthe second lens L2 is f₂, the focal length of the third lens L3 is f3,the focal length of the fourth lens L4 is f₄, the focal length of thefifth lens L5 is f5, the focal length of the sixth lens L6 is f₆, andthe focal length of the seventh lens L7 is f₇ in the imaging lens system11. Each focal length is calculated using a light ray with a wavelengthof 588 nm.

TABLE 12 Example 4 Property Item Value Unit F No 2.0 — Optical length18.003 mm Whole system f 1.566 mm f₁ −7.845 mm f₂ −4.020 mm f₃ 8.521 mmf₄ 5.007 mm f₅ −4.759 mm f₆ 6.732 mm f₇ −22.882 mm f₁₂ 2.088 mm f₂₃−22.055 mm f₃₄ 3.945 mm f₄₅ 5.435 mm f₅₆ 8.068 mm f₆₇ 9.394 mm f₄/f3.198 f₅/f −3.04

As described above, in the imaging lens system of the example 4, becausethe fourth lens that is immediately next to the aperture stop is a glasslens, it is possible to widely set the refractive index and the Abbenumber and thereby facilitate the correction of aberrations, andtherefore the lenses other than this lens can be plastic lenses, whichmakes it possible to simultaneously achieve a high resolution necessaryfor sensing, a size small enough to be mounted on a vehicle, and a lowprice. Further, in the imaging lens system of the example 4, the rangeof f4/f and the range of the Abbe number v4 of the fourth lens may bethe same as those in the imaging lens system of the example 1. Further,the imaging lens system of the example 4 also has the same effects asthe imaging lens system of the example 1.

Example 5: Imaging Lens System

FIG. 9 is a sectional view of an imaging lens system according to anexample 5. In FIG. 9, an imaging lens system 11 includes, sequentiallyfrom the object side, a first lens L1 having a negative power and beingconcave on the image side, a second lens L2 having a negative power andbeing concave on the image side, a third lens L3 having a positive powerand being convex on the object side, an aperture stop STOP, a fourthlens L4 having a positive power and being convex on the image side, afifth lens L5, a sixth lens L6 whose object side is bonded to the imageside of the fifth lens, and a seventh lens L7 having a negative powerand being convex on the image side. Further, the imaging lens system 11includes an IR cut filter 12. IMG indicates an imaging plane.

The property data of the imaging lens system 11 is describedhereinafter.

First, Table 13 shows lens data of each lens surface in the imaging lenssystem 11. In Table 13, the curvature radius, the surface-to-surfacedistance, the refractive index, and the Abbe number are shown as lensdata. The surface denoted by the symbol “*” indicates an asphericsurface.

TABLE 13 Lens Parameter Surface-to- nd Curvature surface (Refractive vd(Abbe radius distance index) number) 1st surface 15.907 1.000 1.804 46.52nd surface 4.399 2.475 3rd surface 15.517 1.250 1.545 56.2 * 4thsurface 1.868 1.702 * 5th surface 40.237 2.536 1.661 20.4 * 6th surface−6.709 0.622 * (STOP) 7th INFINITY 0.030 surface 8th surface INFINITY0.560 9th surface −21.799 1.863 1.553 71.7 * 10th surface −2.541 0.184 *11th surface 19.877 1.645 1.661 20.4 * 12th surface 2.818 0.020 1.50251.0 * 13th surface 2.818 2.995 1.545 56.2 * 14th surface −3.999 0.100 *15th surface −10.662 0.630 1.545 56.2 * 16th surface −86.200 0.100 *17th surface INFINITY 0.700 1.517 64.2 18th surface INFINITY 1.592

Table 14 shows aspheric coefficients for defining the aspheric shape ofan aspheric lens surface in the imaging lens system 11 of the example 5.In Table 14, “−6.522528E-03” means “−6.522528×10⁻³”, for example.

TABLE 14 Aspheric coefficients 3rd surface 4th surface 5th surface 6thsurface 9th surface 10th surface k   0.000000E+00 −0.5946923 0  0.000000E+00   0.000000E+00 −0.007678857 α4 −3.193416E−03  1.097151E−03   5.392646E−03   8.431665E−03 −8.000093E−03  5.197852E−03 α6   9.554737E−05 −1.140715E−03 −2.128120E−04−1.865906E−03 −7.418117E−04 −4.336630E−04 α8 −1.084261E−06 −2.692835E−06  1.109395E−04   1.096699E−03 −3.789986E−04   4.248710E−05 α10−1.623670E−08   0.000000E+00   0.000000E+00 −1.324815E−04   0.000000E+00  0.000000E+00 α12   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00 α12   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00 α16   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00 11th surface 12th surface13th surface 14th surface 15th surface 16th surface k 0 −1.112244E−01−1.112244E−01 0   0.000000E+00 0 α4   2.699705E−03   7.904455E−03  1.090446E−02   2.373828E−02   1.150292E−02 −1.317595E−02 α6  2.101115E−04   2.555279E−04   2.555279E−04 −4.431287E−03 −2.334855E−03  4.001070E−03 α8   0.000000E+00   6.614624E−05   6.614624E−05  6.352887E−04   5.901769E−05 −9.673882E−04 α10   0.000000E+00  0.000000E+00   0.000000E+00 −3.096743E−05   0.000000E+00  9.604736E−05 α12   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00 −3.354162E−06 α12   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00  1.175249E−09 α16   0.000000E+00   0.000000E+00   0.000000E+00  0.000000E+00   0.000000E+00   0.000000E+00

FIG. 10A is a longitudinal aberration diagram of the imaging lens systemin the example 5. FIG. 10B is a field curvature diagram of the imaginglens system in the example 5. FIG. 10C is a distortion diagram of theimaging lens system in the example 5. As shown in FIGS. 10A to 10C, thehalf angle of view is 99°, and the F-number is 2.0 in the imaging lenssystem 11 of the example 5. In the longitudinal aberration diagram ofFIG. 10A, the horizontal axis indicates a position where a light rayintersects the optical axis Z, and the vertical axis indicates a heightof pupil diameter.

In the field curvature diagram of FIG. 10B, the horizontal axisindicates a distance along the optical axis Z, and the vertical axisindicates the image height (angle of view). Further, in the fieldcurvature diagram of FIG. 10B, Sag indicates the curvature of field on asagittal plane, and Tan indicates the curvature of field on a tangentialplane. As shown in the field curvature diagram of FIG. 10B, thecurvature of field is corrected appropriately in the imaging lens system11 of this example. The imaging lens system 11 thereby achieves a highresolution.

In the distortion diagram of FIG. 10C, the horizontal axis indicates theamount of distortion (%) of an image, and the vertical axis indicatesthe image height (angle of view). The field curvature diagram of FIG.10B and the distortion diagram of FIG. 10C show results of simulationusing a light ray with a wavelength of 588 nm.

Table 15 shows results of calculating property values of the imaginglens system 11 of the example 5. Table 15 shows the property values (acombined focal length f₁₂ of the first lens L1 and the second lens L2, acombined focal length f₂₃ of the second lens L2 and the third lens L3, acombined focal length f₃₄ of the third lens L3 and the fourth lens L4, acombined focal length f₄₅ of the fourth lens L4 and the fifth lens L5, acombined focal length f₅₆ of the fifth lens L5 and the sixth lens L6,and a combined focal length f₆₇ of the sixth lens L6 and the seventhlens L7), f₄/f, and f₅/f when the focal length of the whole lens systemis f, the focal length of the first lens L1 is f₁, the focal length ofthe second lens L2 is f₂, the focal length of the third lens L3 is f₃,the focal length of the fourth lens L4 is f₄, the focal length of thefifth lens L5 is f₅, the focal length of the sixth lens L6 is f₆, andthe focal length of the seventh lens L7 is f₇ in the imaging lens system11. Each focal length is calculated using a light ray with a wavelengthof 588 nm.

TABLE 15 Example 5 Property Item Value Unit F No 2.0 — Optical length20.004 mm Whole system f 1.561 mm f₁ −7.865 mm f₂ −4.026 mm f₃ 8.894 mmf₄ 5.026 mm f₅ −5.168 mm f₆ 6.775 mm f₇ −22.386 mm f₁₂ −2.098 mm f₂₃−18.434 mm f₃₄ 4.001 mm f₄₅ 5.293 mm f₅₆ 7.866 mm f₆₇ 9.566 mm f₄/f3.219 f₅/f −3.31

As described above, in the imaging lens system of the example 5, becausethe fourth lens that is immediately next to the aperture stop is a glasslens, it is possible to widely set the refractive index and the Abbenumber and thereby facilitate the correction of aberrations, andtherefore the lenses other than this lens can be plastic lenses, whichmakes it possible to simultaneously achieve a high resolution necessaryfor sensing, a size small enough to be mounted on a vehicle, and a lowprice. Further, in the imaging lens system of the example 2, the rangeof f4/f and the range of the Abbe number ν4 of the fourth lens may bethe same as those in the imaging lens system of the example 1. Further,the imaging lens system of the example 2 also has the same effects asthe imaging lens system of the example 1.

Example 6: Example of Application to Imaging Device

FIG. 11 is a sectional view of an imaging device according to an example6. An imaging device 20 includes an imaging lens system 11 and an imagesensor 21. The imaging lens system 11 and the image sensor 21 are housedin a casing (not shown). The imaging lens system 11 is the imaging lenssystem 11 described in the first embodiment.

The image sensor 21 is an element that converts incident light into anelectrical signal, and a CD image sensor, a CMOS image sensor or thelike is used, for example. The image sensor 21 is placed at an imagelocation in the imaging lens system 11. Note that the horizontal angleof view is the angle of view corresponding to the horizontal directionof the image sensor 21.

It should be noted that the present invention is not limited to theabove-described examples and may be varied in many ways within the scopeof the present invention. For example, the example 6 may be applied toExamples 2 to 5. Further, although the lens 7 is preferably a lenshaving a negative power, the lens 7 is a lens for correcting a field,and the field correction can be made with a positive power. Thus, thelens 7 may be a lens having a positive power.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2017-175546, filed on Sep. 13, 2017, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   11 IMAGING LENS SYSTEM-   12 CUT FILTER-   20 IMAGING DEVICE-   21 IMAGE SENSOR-   L1, L2, L3, L4, L5, L6, L7 LENS

The invention claimed is:
 1. An imaging lens comprising, sequentiallyfrom an object side: a first lens having a negative power and beingconcave on an image side; a second lens having a negative power andbeing concave on the image side; a third lens having a positive powerand being convex on an object side; an aperture stop; a fourth lenshaving a positive power and being convex on the image side; a fifthlens; a sixth lens whose object side is bonded to the image side of thefifth lens; and a seventh lens having a negative power and being convexon the image side, wherein the fourth lens is an aspheric glass lens. 2.The imaging lens according to claim 1, wherein the fourth lens has thehighest power out of lenses having a positive power among the first lensto the seventh lens.
 3. The imaging lens according to claim 1, wherein afollowing expression (2) is satisfied:2.8<f4/f<3.5  (2) where a focal length of the fourth lens is f4 and afocal length of an entire lens optical system is f.
 4. The imaging lensaccording to claim 1, wherein a following expression (1) is satisfied:−3.0<f5/f←2.2  (1) where a focal length of the fifth lens is f5 and afocal length of an entire lens optical system is f.
 5. The imaging lensaccording to claim 1, wherein the image side of the fifth lens and theobject side of the sixth lens each have an aspheric shape.
 6. Theimaging lens according to claim 1, wherein the second lens, the thirdlens, the fifth lens, the sixth lens and the seventh lens are plasticlenses.
 7. An imaging device comprising: an imaging lens systemaccording to claim 1, a flat-plate cover glass placed on an object sideof the imaging lens system; and an image sensor placed at an imagelocation of the imaging lens system.